body{
    height: 100vh;
}
/*底部工具栏*/
nav{
    /*固定在底部*/
    position: fixed;
    width: 100vw;
    z-index: 9999;
    background-color: #ffffff;
    height: 8.5vh;
    border-top: 1px solid gray;
}
ul.toolbar{
    /*弹性布局*/
    display: flex;
    justify-content: space-around;
    align-items: center;
}
.toolbar li span{
    display: block;
}
